1. Field of the Invention.
The invention relates to the field of photography and in particular to a film spool for use in a film cassette and having indicator means for informing the photographer that a film strip inside the cassette has been fully exposed.
2. Description of the Prior Art
In conventional 35 mm film cassettes such as manufactured by Eastman Kodak Co. or Fuji Photo Film Co., Ltd.,(hereinafter referred to respectively as "Kodak" and "Fuji") the film strip is wound on a flanged spool which is rotatably supported within a cylindrical shell. A leading portion of the film strip, termed the "film leader", normally protrudes from a light-trapped slit or mouth of the cassette shell. The spool has a first (normally upper) recessed end engageable by rewinding means, and has a second (normally lower) end with a projection rotatable in a recess in the camera. After insertion of the cassette, the film leader is pulled out and attached to the take-up spool, and is wound on the latter spool by winding means as frames of the film are exposed. When all the film has been exposed, the take-up spool is released from the winding means and the rewinding means is used to rewind the film into the cassette.
Normally, it is assumed that a film cassette with a projecting film leader is unexposed, and that when the leader is fully wound into the cassette the film has been exposed. However, this assumption is not correct in the following situations:
1) An exposed film strip is not fully wound into the cassette. Such a film strip may inadvertently be re-used, causing double exposure, meaning that the photographer loses two sets of photographs. PA1 2) A film strip may be rewound by accident, when it is unexposed, or only partially exposed. This can easily occur with automatic cameras, if the wrong button is pressed. It is possible retrieve a film strip from a cassette using a tool, but if this is not done immediately the unexposed film may inadvertently be sent for processing. PA1 3) Due to improper loading, a film strip may not be engaged by a wind-up spool, and the unexposed film may be removed from the camera and sent for processing when the photographer has taken the expected number of frames, as indicated by a counting device on the camera. PA1 U.S. Pat. No. 4,887,110, issued Dec. 12, 1989; PA1 U.S. Pat. No. 4,894,673, issued Jan. 16, 1990; PA1 U.S. Pat. No. 4,947,197, issued Aug. 7, 1990; PA1 U.S. Pat. No. 4,965,600, issued Oct. 3, 1990; PA1 U.S. Pat. No. 4,978,985, issued Dec. 18, 1990; PA1 U.S. Pat. No. 4,994,833, issued Feb. 19, 1991; PA1 U.S. Pat. No. 4,998,123, issued Mar. 5, 1991; PA1 U.S. Pat. No. 5,003,334, issued Mar. 26, 1991.
While some prior art patents address the double exposure problem, none provides a simple spool, for use in a standard camera and using standard film, which automatically indicates whether or not the film strip it carries has been fully exposed.
U.S. Pat. No. 4,338,015, which issued Jul. 6, 1982, to Polaroid Corp., suggests a spool which has a threaded shaft and nut arrangement together with an exposure-indicating pin mounted within one end of the spool. When the film strip is fully exposed the pin is moved by the nut to a visible location to indicate complete exposure. However, this is fairly complex mechanically, and has the drawback that it requires different spools for different lengths of film. Also, to allow the film strip to unwind freely during processing after the film strip is re-wound in the film cassette it seems that special tools would be required.
U.S. Pat. No. 5,032,862, which issued Jul. 16, 1991 to Behnke, and U.S. Pat. No. 5,264,886, which issued Nov. 23, 1993 to Byrd, show simple devices which indicate whether or not a cassette has been put into a camera. However, these do not indicate whether the film strip has been fully exposed.
A series of patents has issued to Kodak describing a type of cassette which, unlike conventional cassettes, can be operated to automatically advance a film leader out of the cassette shell by rotating the film spool in the unwinding direction. In this case the basic cassette itself provides no indication of whether the film has been exposed. The Kodak patents describe various exposure indicators which may be used with these cassettes to provide a warning that the film was exposed. In some cases a manually movable indicator is used. In others the film strip has notches which allow it to move transversely of the film exit slot after it has been fully exposed. In others, a special camera mechanism is capable of moving an indicator on the cassette when full exposure has occurred. Representative Kodak patents showing these arrangements are as follows:
All of these cassettes appear to be designed for special automatic cameras which have winding means to advance the film out of the spool, and are not designed to be hand-loaded. Also, the film is different from the conventional 35 mm. film, in that the leader end has a full width, and so cannot be used on the more conventional types of cameras.
Fuji has U.S. Pat. Nos. 5,115,268, issued May 19,1992, and 5,278,600, issued Jan. 11, 1994, directed to special spools, which again are of the type in which the film is advanced out of the spool by the unwinding mechanism. Again they seem to require special cameras.